A heavy army presence in the southern Nigerian town of Warri appears to be maintaining an uneasy calm following days of intense fighting between local militia.

More than 30 people have been killed, scores injured and thousands made homeless in the political and ethnic clashes.

The BBC's Dan Isaacs in Warri says the town is unnaturally quiet - but that the grievances that led to the crisis remain unresolved.

The violence between the Ijaw and Itsekiri people - two of the main ethnic groups in the oil-rich Delta region of Nigeria - has been the worst since March, when several multi-national oil companies were force to halt their operations.

Criminal link?

The Delta State governor James Ibori arrived in Warri on Wednesday to try to resolve the crisis.

Following talks with the warring communities he told reporters he hoped both sides would heed his appeal to lay down their arms.

He said he understood that some communities felt excluded from the economic benefits of the oil rich delta region but said the solution lay in dialogue and not armed confrontation.

The Ijaw perceive the Itsekiri to have been favoured by both the government and multi-national oil companies operating in the area.

But our correspondent says many people in Warri believe the real dispute is about which of the heavily armed groups controls the illegal trade in stolen crude oil.

Industry analysts estimate that at least 100,000 barrels of oil are diverted from official exports every day - rich pickings for the criminal underworld, using ethnic rivalries as an excuse for gang warfare.

Shell has advised its office staff not to turn up for work for the time being, but said oil-production had not been disrupted.

Following the violence in March, the oil companies evacuated most of their operational staff from the area, drastically cutting back production.

Some of that output has subsequently been restored, but these latest clashes are once again causing concern over the impact they will have on Nigeria's oil industry.